Battery Life Calculator — Runtime from mAh and Current Draw
Enter your battery capacity in mAh and your device's average current draw in mA to find out how long the battery will last — in total hours and days of typical daily use.
mAh
mA
h/day
%
25 h of continuous use at this draw rate
- 1
Usable capacity
5,000 mAh × 100% ÷ 100 = 5,000 mAhOnly the charge from the starting level to empty is available. - 2
Total runtime
5,000 ÷ 200 mA = 25
How does this calculator work?
Runtime (hours) = Capacity (mAh) ÷ Current draw (mA). A 5 000 mAh battery draining at 200 mA lasts 25 hours, or about 3 days at 8 h/day active use. Divide total hours by your typical daily usage hours to get days per charge. Aging, temperature and variable load will reduce real-world figures.
Formula
How this is calculated
Battery runtime follows directly from Ohm's law of charge: time (hours) = charge (mAh) ÷ current (mA). If a battery holds 5 000 mAh and a device draws 200 mA continuously, the theoretical runtime is 25 hours. In practice, battery chemistry means performance degrades as voltage drops near empty — manufacturers typically rate capacity to 80% of the original after 500 charge cycles, so real-world runtimes are somewhat shorter than the calculation for aged batteries.
Current draw varies enormously with usage. A smartphone in standby might draw 5–20 mA; with the screen on it might pull 200–400 mA; streaming video over LTE can exceed 600 mA. The calculator uses a single average figure — for mixed usage, estimate a weighted average (e.g. 4 hours screen-on at 300 mA + 4 hours standby at 15 mA = average ~158 mA over 8 hours).
The C-rate (current ÷ capacity) shows how quickly the battery is draining relative to its size — a 0.04C rate (200 mA from 5 000 mAh) is a gentle, slow discharge. High C-rates above 1C (discharging the full pack in under an hour) reduce effective capacity and generate heat.
Frequently asked questions
Check the manufacturer's specification sheet ("battery life" tests sometimes list wattage — divide by battery voltage to get mA). Alternatively, use a USB power meter inline with the charger to measure draw directly. For IoT projects, a multimeter in series measures current accurately.
Several factors reduce real-world runtime: battery aging (capacity fades with charge cycles), temperature (cold reduces capacity significantly), variable load (screen brightness, GPS, wireless radios spike current), and the battery protection circuit cutting off at ~3% residual charge to prevent deep discharge.
Most modern smartphones aim for 8–12 hours of screen-on time with typical mixed usage. Flagship devices with 5 000 mAh batteries and efficient 4 nm chips achieve 10–15 hours. A phone drawing 250 mA average from a 4 500 mAh battery delivers 18 h runtime — but real screen-off standby current is much lower, extending days-to-charge substantially.
TG we-Calculate Editorial Team. (2026). Battery Life Calculator — Runtime from mAh and Current Draw [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/battery-life-calculator
TG we-Calculate Editorial Team. "Battery Life Calculator — Runtime from mAh and Current Draw." TG we-Calculate. 2026. https://we-calculate.com/calculator/battery-life-calculator.
TG we-Calculate Editorial Team, "Battery Life Calculator — Runtime from mAh and Current Draw," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/battery-life-calculator
@misc{wecalculate_battery_life_calculator, title = {Battery Life Calculator — Runtime from mAh and Current Draw}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/battery-life-calculator}}, year = {2026}, note = {TG we-Calculate} }
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